1. Field of the Invention
The present invention generally relates to an improvement of a vertical-type air-cooled OHV engine in which a valve operating system is configured to drive intake and exhaust valves provided in a cylinder head to open and close and, more particularly, toward such an engine having a more even cooling of the intake and exhaust valves.
2. Description of the Related Art
Vertical-type air-cooled OHV engine are known, as disclosed in Japanese Patent Application Laid-open No. 59-70838.
In such a vertical-type air-cooled OHV engine, horizontally arranging a cylinder head and a cylinder block continuous with a crankcase makes it possible to achieve a low overall height, thereby achieving a low center of gravity. Accordingly, such an engine is useful as a general purpose engine which serves as a power source for a lawn mower and other various work machines.
However, in a conventional vertical-type air-cooled OHV engine, a cooling fan is attached to an upper end portion of a crankshaft and cooling air generated by the cooling fan flows downward from an upper face side of the cylinder head, which is on the same side as the cooling fan. However, since intake and exhaust valves are vertically arranged side by side in the cylinder head, one of the intake and exhaust valves that is closer to the upper face of the cylinder head against which the cooling air strongly blows is cooled well, but the cooling performance of the other one of the intake and exhaust valves located on a lower side deteriorates.